Yoga Anatomy

Dynamics of breathing 15

The abdominal muscles that have the most direct effect on breathing are the ones
that attach at the same place as the diaphragm, the transversus abdominis. This deepest
layer of the abdominal wall arises from the costal cartilage at the base of the rib cage’s
inner surface. The fibers of the transversus abdominis are interdigitated (interwoven) at
right angles with those of the diaphragm, whose fibers ascend vertically, whereas those
of the transversus abdominis run horizontally (see figure 1.15). This makes the transversus
abdominis the direct antagonist to the diaphragm’s action of expanding the rib cage. The
same layer of horizontal fibers extends this action upward into the posterior thoracic wall
as the tranversus thoracis, a depressor of the sternum.
The other layers of the abdominal wall have similar counterparts in the thoracic cavity.
The external obliques turn into the external intercostals, and the internal obliques turn into
the internal intercostals (see figure 1.16). Of all these thoracoabdominal layers of muscle,
only the external intercostals are capable of increasing thoracic volume. All the others pro-
duce a reduction of thoracic volume, either by depressing the rib cage or pushing upward
on the upper attachments of the diaphragm.

E5267/Kaminoff/fig1.16/417565/alw/pulled-r3

External

intercostals

External

oblique

Internal

oblique

Transversus

abdominis

Internal

intercostals

Innermost

intercostals

Transversus

thoracis

E5267/Kaminoff/fig1.17/417566/alw/pulled-r3

Transversus thoracis

Diaphragm

Transversus abdominis

Figure 1.16 The continuity of the abdominal and intercostal layers shows how (a) the external

obliques turn into the external intercostals, (b) the internal obliques turn into the internal intercos-

tals, and (c) the transversus abdominis turns into the transversus thoracis and innermost intercos-

tals.

Figure 1.15 Posterior view of
the chest wall, showing the inter-
digitated origins of the diaphragm
and transversus abdominis form-
ing perfect right angles with each
other. This is clearly an agonist–
antagonist, inhalation–exhalation
muscle pairing that structurally
underlies the yogic concepts of
prana and apana.

a b c